Laminated magnetic core



June 20 1961 u. KRABBE 2,989,712

LAMINATED MAGNETIC CORE Filed Nov. 26, 1957 v 2 Sheets-Sheet .1

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LAMINATED MAGNETIC CORE Filed Nov. 26, 1957 2 Sheets-Sheet 2 Fig.9

INVEN TOR.

Y (/LF/K KRHBBE United States Patent 2,989,712 LAMINATED MAGNETIC CORE Ulrik Krabbe, Helsingor, Denmark, assignor to Allmanna Svenska 'Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Filed Nov. '26, 1957, Ser. No. 699,099 Claims priority, application Sweden Nov. 29, 1956 6 Claims. (Cl. 336-217) The present invention relates to a laminated magnetic core intended for especially exacting applications, for instance for transductors (magnetic amplifiers). In such cases it is important that the reluctance of the core is as low as possible and that the magnetizing curve has the sharpest possible knee. For this reason the core should be so arranged that local saturation cannot arise. These properties can either be obtained by means of closed ring cores or by cores made from straight leg or yoke laminations being so arranged that they form over-lap joints with each other. Both these types, of course, make it possible to use grain-oriented magnetic material.

The core material is well utilized in wound cores and it is possible to obtain an iron space factor of mainly 100% in the leg portions as well as the yoke portions. Considerable difliculties are present, however, when applying the windings on such cores. Laminated cores with over-lap joints cannot, without special measures, give a higher space factor in the core legs than 50%, but such cores are advantageous because it is easy to apply the windings to them. The common way of obtaining a higher space factor than 50% in the legs, is to make the core with a yoke width which is twice the leg width, it will then be possible to conduct the magnetic flux from two leg laminations to each half of an intermediate yoke lamination and in that way the space factor in the legs will be 67%.

However, a double yoke width would be unsuitable with larger magnetic cores and the present invention relates to a magnetic core having single yoke width, but nevertheless allowing a higher space factor than 50% in the legs. The main feature of the invention is that all leg laminations and yoke laminations, in pairs, form over-lap joints having mainly triangular form, such a core will fulfil the primary demand that the flux will not have to be conducted through butt joints.

The invention prevents any part of the core from being saturated earlier than the legs, irrespective of the type of material used in its manufacture. This result is obtained by arranging every leg lamination in over-lap joint with a respective yoke lamination. The joint surface is mainly larger than the sectional surface of a leg lamination or a yoke lamination. It is generally true that the larger the width of a leg lamination or a yoke lamination in relation to the thickness of these laminations, the less the air gaps in the over-lap joints will influence the reluctance of the core. By making the core from rectangular laminations it is possible to use first-class grain oriented material and at the same time, to use pre-wound coils.

In the circumstances, according to the invention, an advantage is that all the available square or rectangular contact surface between a leg lamination and a yoke lamination, is not utilised to form the over-lap joint, but that the joint surface is mainly triangular and this constitutes the advantage that two pairs of joint forming leg and yoke laminations can be so arranged that the leg lamination of one pair will be situated in the same layer as the yoke lamination of the other pair. The triangular joint surfaces of both pairs will, together, form the above mentioned total available contact surface. Apparently a butt joint is then obtained between two laminations, the ends of which are cut obliquely. It must be observed, how- Patented June 20, 1961 ice ever, that this butt joint will never carry flux. From the manufacturing, as well as functional points of view, it is most suitable that the ends of the laminations lying in the same layer are cut across a straight line and that the laminations form a butt joint along this line. Principally this line does not have to be straight but can have any arbitrary form. The butt joint should have a main direction from the outer to the inner corners of the readymade core.

It is usually sufiicient that the leg laminations and the yoke laminations have the same Width and in such cases some of the laminations will have to be cut across a 45 line. It may be required that the yoke laminations have a slightly larger Width than the leg laminations so that the yokes are saturated by a larger flux than the legs. In such cases the cuts of the laminations can either be made across a line deviating from 45, in which case the total contact surface of the corner of the core will be rectangular or 45 cuts can be used, in which case the contact surface will be square. The invention will now be described by way of example with reference to the accompanying drawings, in which,

FIG. 1 shows the principle of stacking yoke and leg laminations,

FIGS. 2 to 6 show different ways of cutting certain laminations, and

FIGS. 7 to 9 show cores according to the invention.

FIG. 1 shows two pairs of yoke and leg laminations. It can be assumed that 1 designates a yoke lamination being in over-lap contact with a leg lamination 2, while 3 designates another yoke lamination in over-lap contact with the leg lamination 4. In both pairs, one of the laminations is cut obliquely. In the first pair the yoke lamination 1 is cut across a straight line coinciding with the dotted line 5 on the leg lamination 2, in the other pair the leg lamination 4 is cut across a straight line coinciding with the dotted line 6 on the yoke lamination 3. Each pair of laminations will thus obtain triangular overlap joints. Owing to the oblique cutting of two of the laminations it will be possible to put the two pairs together in such a way that the yoke lamination 1 and the leg lamination 4 are situated in the same layer and have their obliquely cut ends in butt joint with each other,

Provided that the over-lap joints are sufiiciently large to transfer the magnetic flux between legs and yokes the reluctance of the core will not be increased. It is thus evident that the apparent butt joint will not carry any flux.

In FIG. 2, one corner of the core is shown in which the leg lamination 7 has the same width as the yoke lamination 8. The latter lamination is obliquely cut in the shown corner and the cutting line 9 divides the square contact surface across a 45 line. In FIG. 3 it is shown that the cutting line 10 does not necessarily have to be a straight line. It can be wave-formed according to the figure or it can be tooth formed or curved or it may have any arbitrary form. However, one condition is that the cutting line mainly extends between the outer and inner corners of the core so that there is a chance of every longitudinal strip 7, 7" of a lamination meeting a longitudinal strip 8', 8" of the lamination with which it is in butt joint.

FIGURES 4 to 6 show three diiferent ways of cutting the laminations when the width of the yoke laminations 11 exceeds the width of the leg laminations 7.

The total contact surface will be rectangular (a-b) and according to FIG. 4 the cutting line 12 may extend diagonally, in which case the cutting angle differs from 45. The 45 cut could also be obtained extending from the inner corner of the ready-made core (line 13 in FIG. 5) or from its outer corner (line 14 in FIG. 6).

The different forms according to FIGS. 7 to 9 difier 3 from each other in that a number of differently shaped laminations have been used. In FIG. 7 four different laminations are used, in FIG. 8 three different laminations and in FIG. 9 only two different laminations.

In FIG. 7, the laminations 1 and 16 represent yoke laminations situated in the same layer. The underlying layer comprises a frame composed of yoke laminations 17, 1 8 and leg laminations 19, 211'. The leg and yoke laminations in the frame form butt joints with each other. The next layer comprises two leg laminations 20", 21. The fourth layer comprises two yoke laminations 22, 23 and in the next layer another frame is situated, built up from the yoke laminations 24, 25 and the leg laminations 26, 27. The bottom layer in the figure shows two leg laminations 28, 29. In this way, the core is built up until the desired thickness has been obtained.

By utilizing the principle shown in FIG. 1 in each corner, a core will be obtained having an iron space factor in the legs of 67%. The yoke lamination 15 thus forms an over-lap joint with a leg lamination 19 and the yoke lamination 17, lying in the same layer as the leg lamination 19, forms an over-lap joint with the leg lamination 211". In this case, yoke laminations 15 and 22 are used, both ends of which are cut at mainly right angles and yoke laminations 17, 24 are used, both ends of which are cut obliquely. The leg laminations 20" and 28, 19 and 26 respectively, are cut in a corresponding way.

In FIG. 8, the stacking principle of a core is shown, where all leg laminations have the same form, the yoke laminations being still of two different types. One of the ends of the leg laminations is cut at right angles and the other end is cut obliquely. One unit of the core consists of a yoke lamination 30 in one layer, leg laminations 31, 32 in butt joint with a yoke lamination 33, in the under lying layer, leg laminations 34, 35 in butt joint with the yoke lamination 36 in the next layer, the yoke laminations 33 and 36 being parts of opposite yokes, finally, the yoke lamination 37 in a following layer. Another unit of the core is shown, comprising a yoke lamination 38 in the same layer as the yoke lamination 37, the laminations 39, 41 41 in the following layer and the laminations 42, 43, 44 in the underlying layer and is completed with a yoke lamination 45 in a further layer. The space factor will also, in this case, be 67%.

In FIG. 9, only one type of yoke lamination and one type of leg lamination are used. Both types of laminations are cut at right angles at one end and are cut obliquely at the other end. The obliquely c-ut ends of a leg lamination (-46, 48) and a yoke lamination (47, 49 respectively) form a butt joint with each other, the core is built up in such a way that said butt joint, in two adjacent layers, is moved to the next following corner of the core. The ends of two leg laminations or yoke laminations, cut at right angles, are turned in different directions (46, 48 or 49, 50). In the uppermost layer the butt joint 51 is situated in the nearest lefthand corner of the core, in the next layer the butt joint 52 is situated in the farthest lefthand corner, in the following layer the butt joint 53 is situated in the farthest right hand corner and so on. When the core is pressed together three layers will comprise two leg or yoke laminations and the iron space factor of the whole core will be 67%.

If it is possible, without inconvenience, to allow a double yoke width, the suggested stacking principle can also be used to obtain a higher iron space factor in the legs. The type shown in FIG. 7 may be used to give a core with an space factor. In that case groups of yoke and leg laminations are used stacked in accordance with the three top layers or the three bottom layers of FIG. 7. On such a group, with its yoke laminations turned upwards a new group is placed with the yoke laminations turned downwards and displaced one yoke width in the longitudinal direction of the legs. In this way a group will be obtained having four leg laminations in five layers, such groups are stacked together until the core has obtained the desired thickness. Some of the yoke laminations will have to be supported by means of strips of non-magnetic material placed in the core.

I claim as my invention:

1. A laminated magnetic core comprising at least two parallel leg members joined at their respective ends by a pair of yoke members, said members each being built of layers of straight strip laminations, in each corner of the core certain layers comprising a leg lamination and a yoke lamination having oblique ends abutting substantially along the diagonal of said corner, each of said layers being surrounded on one side by and in contact with a second layer including in said corner a leg lamination only having a square end forming a substantially triangular lap joint with the yoke lamination in said oblique-ended layer, and on the other side by and in contact with a third layer including in said corner a yoke lamination only having a square end forming a substantially triangular lap joint with the leg lamination in said oblique-ended layer, said leg lamination of the second layer contacting and forming in said corner a lap joint with the yoke lamination of the third layer of the next succeeding oblique-ended layer.

2. A laminated magnetic core structure according to claim 1, in which one of the ends of every leg and yoke lamination is cut mainly at right angles and that the other end is cut mainly obliquely.

3. A laminated magnetic core according to claim 1, in which every other lamination in both the legs and yokes is cut obliquely at both ends and every intermediate lamination is cut at right angles at both ends.

4. A laminated magnetic core according to claim 1, in which every other lamination in the yoke is cut obliquely at both ends and every intermediate lamination is cut at mainly right angles at both ends, all leg laminations are cut obliquely at one end and at mainly right angles at the other end.

5. A laminated magnetic core according to claim 1, having in each corner oblique lamination ends of two consecutive joints disposed in the same layer.

6. A laminated magnetic core according to claim 1, in which the yoke laminations and the leg laminations are of substantially the same width.

References Cited in the file of this patent UNITED STATES PATENTS 1,394,121 Sclater Oct. 18, 1921 2,797,396 Granfield June 25, 1957 FOREIGN PATENTS 77,835 Denmark July 19, 1954 699,549 Great Britain Nov. 11, 1953 735,228 Great Britain Aug. 17, 1955 

